The demand for rigid decorative flooring materials such as ceramic and masonry tiles and wood laminate flooring in the construction industry has grown over recent years. These materials are, among other qualities, durable, easy to maintain, and attractive. However, despite their numerous desirable qualities, these materials typically exhibit poor acoustic properties with regard to structure-borne sound transmission. Specifically, the noises generated by footfalls or other periodic impacts are readily transmitted to other parts of the building—especially the rooms below. Poor sound or acoustic properties are extremely undesirable in all structures, but in particular in high-rise office buildings, hotels, apartments, and the like.
Impact noise isolation is a current building design issue as evidenced by the fact that almost all contemporary model building codes establish a minimum impact noise isolation between occupied living units. Actual acoustical performance is determined by test procedures developed by either the International Standards Organization (ISO) or the American Society of Testing and Materials (ASTM). Within North America, the ASTM test procedure is preferred. The specific ASTM Impact Sound Isolation tests are E492 and E 989. The single number rating generated by these test procedures is an impact isolation class or IIC. The various International Code Council model building codes require that floor/ceiling assemblies be designed to a minimum IIC rating of 50. Advisory agencies such as HUD and private real estate development corporations often recommend IIC performance of 60 or more for luxury dwellings. Typical floor/ceiling systems incorporating rigid decorative flooring materials fall below these requirements, delivering IIC ratings of 30-45. For this reason many resilient underlayment systems have been developed to improve the acoustic performance of floors.
In the prior art an underlayment layer was inserted between the floor slab or structural subfloor and the floor topping layer to improve impact noise isolation. (The terms “slab” and “subfloor” are used interchangeably herein to refer to both a floor slab and a structural subfloor as supporting structure.) These prior art underlayment layers are commonly manufactured as homogeneous substrates that can be rolled or laid onto the subfloor. Most of these materials consist of or include a uniform layer of cellular foam or rubber as disclosed in U.S. Pat. Nos. 2,811,906, 3,579,941, 4,112,176, 5,016,413 and 6,920,723. An example of such a substrate is shown in FIG. 1 from U.S. Pat. No. 6,920,723. Notably, most descriptions of these prior art structures incorrectly credit the cellular composition or resulting internal voids as an acoustic energy dissipating mechanism rather than correctly describing these features as reducing the underlayment's effective dynamic stiffness and thereby improving the impact isolation of the underlayment. If the underlayment material is soft or the void fraction high (resulting in an underlayment that is soft) then the installed sheet is unable to support tile or any other rigid topping material without allowing the tile or rigid topping material to crack. In such cases, a rigid topping layer such as 6-20 mm OSB or plywood is installed on top of the underlayment layer before installing the rigid decorative flooring material. This additional step adds to the installed cost and overall height of the system. In each case, the two opposite surfaces of the homogeneous underlayment layer are parallel and flat. Commercial examples of such underlayment materials include Regupol-QT by Dodge-Regupol of Lancaster, Pa., QuietFoam® underlayment by Quiet Solution of Sunnyvale, Calif., and ETHAFOAM from Dow Chemical of Midland, Mich.
Thin, fibrous mats can also be characterized as homogeneous underlayments. Although such mats lack a cellular structure or predictable void fraction, their material characteristics and limitations are the same. A commercial example of a thin fibrous mat underlayment is ENKASONIC from Akzo Industrial Systems Company of Asheville, N.C.
Other prior art underlayment layers use a homogeneous material that is profiled or coped with engineered voids to reduce the effective dynamic stiffness of the underlayment. Examples are described in U.S. Pat. Nos. 4,759,164, 5,110,660, and 6,213,252. U.S. Pat. Nos. 4,759,164, and 6,213,252 describe a rubber sheet with a bottom surface that includes parallel channels that reduce the overall surface contact area of the underlayment from 100% to a range between 15 and 75%. For example, FIG. 2 from U.S. Pat. No. 5,110,660 shows a rubber mat wherein cavities and intersecting hollow channels (i.e. parallel grooves) are designed to impart the benefits of a soft rubber to a harder base material. A potential problem with the underlayment described by U.S. Pat. No. 6,213,252 is that the parallel grooves may inadvertently align with the parallel edges of the overlying ceramic tile or wood flooring planks allowing the system to form a fissure at the grout, across a tile, or between wood panels. A commercial example of such an underlayment is Neutra-Phone by Royal Mat International, Inc. of Quebec, Canada. In addition, because the grooves penetrate into the underlayment only a small distance relative to the thickness of the underlayment, the dynamic stiffness of the underlayment is not significantly changed from the dynamic stiffness of the bulk material.
A third prior art structure is a composite underlayment. U.S. Pat. Nos. 4,685,259, 5,867,957 and 6,077,613 describe underlayments that involve multiple layers of dissimilar materials to create a composite laminated structure. Such designs incorporate a soft material with a low relative dynamic stiffness and good noise isolation together with a hard material adhered to the top and or bottom surface(s). Though the hard material exhibits poor noise isolation, it allows the rigid decorative flooring material to be directly installed over the underlayment. A more complicated underlayment manufacturing process is exchanged for a more cost effective installation method. Commercial examples of such underlayments include KINETICS Type SR Floorboard from Kinetics Noise Control of Dublin, Ohio and PCI-Polysilent from ChemRex of Minneapolis, Minn.
Thus many underlayments exist for reducing impact noise transmission. Although homogeneous mats exist, they must be unacceptably thin and/or rigid to allow direct installation of an overlaying rigid decorative layer. However, improved impact noise isolation via lower dynamic stiffness and greater mat thickness are structurally insufficient to allow a decorative topping layer such as tile to be directly applied to the underlayment. Without the additional support of a rigid top surface layer, the overlaying tiles or laminated flooring would crack and deform as pressure is applied. The introduction of the support layer further adds to the height requirements, resulting in greater expense.
It would, therefore, be beneficial to provide a noise isolating underlayment which provides adequate acoustical performance while providing the structural support necessary to support the tiles and laminated wood flooring. It would also be beneficial to provide such properties while minimizing the height required for the insulating member.